On 7/22/20 9:39 AM, Christian Borntraeger wrote: > > > On 22.07.20 09:24, Janosch Frank wrote: >> On 7/22/20 8:43 AM, Christian Borntraeger wrote: >>> >>> >>> On 15.07.20 16:08, Janosch Frank wrote: >>>> Normally they don't need to be set up before waiting for an interrupt >>>> but are set up on boot. The BIOS however might overwrite the lowcore >>>> (and hence the PSWs) when loading a blob into memory and therefore >>>> needs to set up those PSWs more often. >>> >>> Now when I read the new comment this actually inidicates a bug. >>> When do we restore the original content? If the loaded program >>> does have interrupt handlers in the original image and relies on that >>> then we are broken, no? >> >> I haven't seen references to a save/restore functionality for those >> PSWs. And I also think it's not that easy to do because we have multiple >> ways of loading data and if we want to print when loading we might end >> up overwriting and then saving the written value for a later restore. >> >> I need to have a closer look at how virtio works, but wouldn't we have a >> chicken - egg problem with IO interrupts for IO that writes the prefix? >> >> The BIOS often has "interesting" solutions to problems. >> If you have a quick fix, be my guest and send it. If not I'd put it on >> my todo list or let Stefan make it a proper dev item. > > Maybe a global fixup table in BIOS memory that restores all the memory that > we messed with when we hand over control? Can you at least change the comment > here to add a fixme?
Sure > >> >>> >>>> >>>> Signed-off-by: Janosch Frank <fran...@linux.ibm.com> >>>> --- >>>> pc-bios/s390-ccw/start.S | 10 ++++++++-- >>>> 1 file changed, 8 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/pc-bios/s390-ccw/start.S b/pc-bios/s390-ccw/start.S >>>> index 01c4c21b26..b0fcb918cc 100644 >>>> --- a/pc-bios/s390-ccw/start.S >>>> +++ b/pc-bios/s390-ccw/start.S >>>> @@ -64,7 +64,10 @@ consume_sclp_int: >>>> stctg %c0,%c0,0(%r15) >>>> oi 6(%r15),0x2 >>>> lctlg %c0,%c0,0(%r15) >>>> - /* prepare external call handler */ >>>> + /* >>>> + * Prepare external new PSW as it might have been overwritten >>>> + * by a loaded blob >>>> + */ >>>> larl %r1, external_new_code >>>> stg %r1, 0x1b8 >>>> larl %r1, external_new_mask >>>> @@ -84,7 +87,10 @@ consume_io_int: >>>> stctg %c6,%c6,0(%r15) >>>> oi 4(%r15), 0xff >>>> lctlg %c6,%c6,0(%r15) >>>> - /* prepare i/o call handler */ >>>> + /* >>>> + * Prepare i/o new PSW as it might have been overwritten >>>> + * by a loaded blob >>>> + */ >>>> larl %r1, io_new_code >>>> stg %r1, 0x1f8 >>>> larl %r1, io_new_mask >>>> >> >>
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